1. Field of the Invention
The present invention relates to the preparation of 2-ethylhexanol and to catalysts for its preparation.
Discussion of the Background
2-Ethylhexanol is used in large quantities as an esterification component, e.g. for the preparation of dioctyl phthalate as a plasticizer for PVC. It is prepared by the hydrogenation of 2-ethylhexenal (oxo successive product).
In this process hydrogenation can occur both in the gaseous phase (DE-AS 11 52 393) and in the liquid phase (DE-AS 19 49 296). In these processes higher catalyst loads can generally be achieved in the liquid phase due to improved dissipation of heat.
In addition to the catalyst load, the purity of the product, expressed, e.g. by its bromine number, is of great interest since the plasticizers to be prepared later must exhibit good color stability.
It is known from DE-AS 19 49 296 that the liquid-phase hydrogenation of 2-ethylhexenal with cyclic processing of the reaction product with a catalyst load of approximately 1.8/h results in a product with a bromine number ranging from 3.9 to 0.2. The catalysts used here have the drawback that despite suitable catalyst loads during hydrogenation, the result is a product that is inadequate in terms of its bromine number and whose degree of purity must be improved by subsequent distillation.
Another process is known from DE-AS 12 69 605 in which, in the liquid phase and with increased pressures and increased temperatures, 2-ethylhexenal is converted to 2-ethylhexanol over nickel and/or cobalt catalysts to which copper and/or chromium and/or manganese has been added. To these catalysts one further adds a pyro- or a polyacid in the free form and/or in the form of at least a salt of the aforementioned metals.
The drawback of this process and catalysts is the need for very high pressures (preferably from 200 to 400 bar) and higher temperatures. Moreover, the catalyst loads of approximately 0.2/h and the high bromine numbers of the product ranging from approximately 0.13 to 0.1 are negative factors for hydrogenation.
The above problems make clear that there is a need for a facile catalytic hydrogenation process which is capable of producing a 2-ethylhexanol product of exceptional purity and low bromine number.